Although combination bed sheets with the under sheet attached to the upper sheet have been proposed numerous times in the prior art, none of the earlier concepts have ever been marketed, to my knowledge.
The reason for this, in my opinion, is that a combination bed sheet must have the possibility of speedy attachment to the mattress and speedy attachment of its upper sheet to its lower sheet, and the capability of speedy detachment of its upper sheet from its lower sheet, and also, a predictable durability for years of service.
The public has had much experience with breakage of zippers. A zipper can become separated, even when its sides are interlocked, provided there is stress on it. The stitchings of a zipper can become torn from adjacent material when there is substantial stress on it, and substantial stress can easily occur in a product of this type, resultant from persons tugging on bed sheets in pulling them toward the head of the bed.
An objective hereof is to provide such a product with a predictably good durability by the provision of pockets on the upper sheet for taking the stress of such sheet tugging so as to relieve the zipper and its stitchings of such stress.
A pocketed upper sheet has been proposed in the prior art in a non-zippered two-sheet combination and hence proposed not for the purpose of protecting a zipper, the pockets proposed being of a non-elastic type. Such a proposal is shown in U.S. Pat. No. 4,344,196, issued Aug. 17, 1982 to Hellen F. Large.
For these reasons, it is an object of this invention to provide a bed sheet combination that is provided with a single zipper extending along the foot of the bed only and with the sides of the sheets free of interconnecting means so that a minimum of unzipping is necessary and speed of unzipping and zipping is possible.
The foot-end portions of the sheets hereof are free of impediments for fast positioning of the sheets into use positions.
A feature not present in the Large patent and present herein is the provision of having the side edges of the upper sheet being capable of extending continuously from the upper pockets toward the head end of a mattress sufficiently as to have the capability of a continuous presence adjacent a sleeper's feet at the sides of the upper sheet.
Another feature not present in Large is elastic upper sheet pockets which are present in this invention to allow for expansion of a pocket during its application to a mattress for speedy installation. Elastic material in upper sheet pockets has been shown in prior art U.S. Pat. No. 3,962,739, issued June 15, 1976 to Lou Anne Crockett. However, in the Crockett patent there is no zipper to protect by means of pockets, and removability of the upper sheet from the lower sheet is not provided for.
Of interest is U.S. Pat. No. 3,857,124, issued Dec. 31, 1974, to Belva D. Hadley for a sleeping bag type of double sheet arrangement, but without pockets to protect the zipper, and without capability of single zipper sheet disconnection and economy and speed of a single zipper at the foot-end.
Also of interest is a U.S. Pat. No. 3,832,743, issued 9-3-74, to Saundra L. Smith, titled BED SHEETS, but lacking pockets to protect the zipper.
Of importance as regards the Crockett patent is the need for seperability. Many women would be reluctant to buy a sheet combination as it would seem to them to be too cumbersome for their washing maching, two sheets at once especially if king-size.
Also non-seperability has a disadvantage because a tear in only one sheet then wastes two sheets.